As a conventional electrophotographic image forming device such as a laser printer, Japanese laid-open patent publication No. 2006-1844553 discloses an image forming device including a photosensitive drum unit provided with a plurality of photosensitive drums, and a developing device unit (developing device tray) provided with a plurality of developing devices. These photosensitive drum unit and developing device unit are configured to be detachably mounted in the main body of the image forming device.
In this image forming device, however, when the developing device unit is being removed from the main body, first the entire developing device unit is necessary to be detached from the photosensitive drum unit for separating the developing rollers of the developing devices from the photosensitive drum unit. The developing device unit is then to be pulled out from the main body. Hence, this image forming device necessitates a large-sized mechanism for supporting the weight of the whole developing device unit as well as for allowing the developing device unit to be movable.